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From "Ryan King (JIRA)" <j...@apache.org>
Subject [jira] Commented: (CASSANDRA-1555) Considerations for larger bloom filters
Date Thu, 25 Nov 2010 23:57:15 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1555?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12935915#action_12935915
] 

Ryan King commented on CASSANDRA-1555:
--------------------------------------

Yeah, you're right, we need to upgrade to the 64bit version.

Our options with backward-compat seem to be:

1) keep 2 separete BF impl's- each with their own bitset and hash function

2) regenerate the BF the first time we start up with this patch

I'd lean towards #2, but am open to other suggestions.

> Considerations for larger bloom filters
> ---------------------------------------
>
>                 Key: CASSANDRA-1555
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1555
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Stu Hood
>            Assignee: Ryan King
>             Fix For: 0.8
>
>         Attachments: cassandra-1555.tgz
>
>
> To (optimally) support SSTables larger than 143 million keys, we need to support bloom
filters larger than 2^31 bits, which java.util.BitSet can't handle directly.
> A few options:
> * Switch to a BitSet class which supports 2^31 * 64 bits (Lucene's OpenBitSet)
> * Partition the java.util.BitSet behind our current BloomFilter
> ** Straightforward bit partitioning: bit N is in bitset N // 2^31
> ** Separate equally sized complete bloom filters for member ranges, which can be used
independently or OR'd together under memory pressure.
> All of these options require new approaches to serialization.

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